* Add support for vs17 builds (for PHP 8.4)
We make the necessary additions to `compute-virtuals.ps1`, where the
choice of the WinSDK is somewhat arbitrary but rather conservative.
* Switch from windows-2019 to windows-2022 runners
This is needed to actually be able to do vs17 builds, since that
requires Visual Studio 2022, which is not available on the windows-
2019 runners. That implies that vc15 builds are no longer possible
without additional changes[1], but that shouldn't be a concern because
none of the supported PHP versions require vc15 builds.
[1] <https://github.com/actions/runner-images/issues/9701>
* Update CMake generators
Since window-2022 uses Visual Studio 2022, we need to update the CMake
generators; using the proper toolset is already catered to by the `-T`
option.
* Bump vs16 Windows SDK to 10.0.20348.0
This solves the stdalign.h issue for ICU 75.1.
`actions/checkout@v3` is deprecated, so we update to v4. We do not
expect any trouble with this update, since we already treated the
upload artifacts as immutable, but nonetheless we did a couple of test
builds (argon2, zlib and libjpeg) and the results appear to be fine.
`actions/checkout@v3` is deprecated, so we update to v4. This is done
without further tests, but a mere search and replace. We do not expect
anything to break, but even if so, we can still fix these issues.
